Early pregnancy loss is a feature of all mammals and is particularly high in women. It is a major public health concern. More than 50% of normally conceived pregnancies fail in the period at about the time the embryo attaches to the uterus and begins to implant. Among the causes are developmental abnormalities of the embryo, weak or late signaling from the trophectoderm (the precursor of the placenta) and an ill- prepared maternal uterus. Here we shall study two aspects of conceptus-maternal relationship in early pregnancy. The first (goal 1) is to define the role of the transcription factor Cdx2 in trophectoderm specification and functional differentiation. Aim 1A is to confirm that Cdx2 plays a key role in the transcriptional control of the genes for the signaling molecule interferon-tau (IFN-T) and other genes characteristically up-regulated in trophectoderm. Aim 1B will test the hypothesis that Cdx2 is necessary in directing trophectoderm emergence in murine and bovine embryos and in maintaining a polarized epithelium. Aim 1C will confirm preliminary studies that Cdx2 is a marker of presumptive trophectoderm as early as the 2-cell stage of development. We shall also determine whether it is an analogous marker of cell fate in the bovine embryo. Goal 2 of this project is to define the function of Sin1, a newly discovered protein that associates with carboxyl end of the cytoplasmic domain of the IFN receptor subunit, IFNAR2. We hypothesize that maternal recognition of pregnancy involves a localized inflammatory response and the modulation of stress pathways in maternal endometrium at the site of implantation, and that Sin1 links the IFN response pathway to signal transduction pathways, including the stress-activated protein kinase (SAPK) pathway. Aim 2A is to define partners for Sin1 in endometrial signaling through the use of a yeast two-hybrid screen. Aim 2B will test the hypothesis that when IFN-T binds to the cell surface of uterine epithelial cells Sin 1 will be recruited, and this event will precede changes in the activities of stress-activated signal transduction pathways. Aim 2C will examine whether there is cellular relocation of Sin1 following IFN-T binding to the cell. Aim 2D will attempt to knock down Sin1 expression by RNAi and, by using this approach, determine whether Sin1 plays a role in some of the varied (pleiotropic) actions of type I IFN on mammalian cells. Aim 2E will explore whether the over-expression of different domains of the Sin1 protein can interfere with normal Sin1 function. Aim 2F is to create Sin1 null mice in order to gain a more complete insight into Sin1 function in the whole animal as well as in uterine endometrium. Together these studies are expected to provide information on two key events in early pregnancy, the formation of an early placenta and immediate maternal responses to the presence of a tiny embryo attaching to her uterine wall.